396 THE FUNGI WHICH CAUSE PLANT DISEASE 



The Dacryomycetales include forms with a gelatinous sporo- 

 phore. They are mostly small, inconspicuous saprophytes, common 

 on decaying wood, leaves, etc. The Hymenogastrales are puff-ball 

 forms, and are very numerous and of very diverse structure. None 

 have been reported as parasitic. The Nidulariales is a small order 

 comprising the curious bird-nest fungi, all saprophytes. The 

 Sclerodermatales are thick-skinned puff balls, mostly subter- 

 ranean, and not known to be parasitic. 



Exobasidiales (p. 395) 



Strictly parasitic, the mycelium penetrating the host and usually 

 causing marked hypertrophy; hymenium imaccompanied by fleshy 

 sporocarp, consisting only of the closely-crowded, clavate basidia 

 which break through the epidermis of the host. 



The basidia bear four, rarely five or six sterigmata and spores. 

 The spores are mostly curved. Conidia are also found in some 

 species. The basidiospores germinate with a germ tube which pro- 

 duces fine sterigmata and secondary spores capable of budding. 

 The hymenial cells are binucleate, the two nuclei of the basidial cell 

 fusing into one basidium-nucleus. This divides mitotically giv- 

 ing rise to the spore nuclei. 



This order among the basidia fungi is analogous to the Exoas- 

 cales among the ascus fungi. There are two genera and some 

 twenty-five species. 



Key to Genera of Exobasidiales. 



Basidia 6-spored; not gall producers 1. Microstroma, p. 396. 



Basidia 4-spored; producing galls 2. Ezobasidium, p. 396. 



Microstroma Niessl. contains only three species of which 



M. album (Desm.) Sacc. is on oak; 



M. juglandis (Ber.) Sacc. on Juglans and Hicoria. 



Ezobasidium Woronin 



Mycelium penetrating the host and causing distinct hyper- 

 trophy, hymenium subcuticular, erumpent, basidia 4-spored, 

 spores elongate. 



There are some twenty species, mostly on members of the 



